Hi:
Web Report Studio uses XML and Java to present information. HTML tags may or may not be honored in a Web Report Studio report or stored process results (usually not with SAS 9.1.3 and WRS 3.1) This Tech Support note has some relevant info:
http://support.sas.com/kb/18/085.html
The type of drill-down that you describe is seems more a Portal applet or Portal stored process rather than a WRS report.
For more help with what you want to accomplish, you might be better served by opening a track with Tech Support.
cynthia